Over the past few years, the demand for ever cheaper and lighter weight portable electronic devices has led to a growing need to manufacture durable, lightweight, and low cost electronic circuits including high density memory chips. The increasing complexity of electronic devices and integrate circuits, coupled with the decreasing size of individual circuit elements, places ever more stringent demands on fabrication processes, particularly with respect to resolution and accuracy of the fabrication patterns. The ability to fabricate on a nanometer scale guarantees a continuation in miniaturization of functional devices. Micro-fabrication techniques can produce structures having features on the order of nanometers. Micro-fabrication is used in a wide variety of applications, such as the manufacturing of integrated circuits (i.e., semiconductor processing), biotechnology, optical technology, mechanical systems, and micro-electro-mechanical systems (“MEMS”).
Micro-fabrication is typically a multi-step process involving the patterned deposition or removal of material from one or more layers that make up a finished device. Micro-fabrication is sensitive to the presence of contaminant particles. In micro-fabrication it is common to inspect a substrate for the presence of contaminants between process steps. As the size of micro-fabricated features decreases, smaller and smaller contaminant particles and films can affect device yield. A number of tools have been developed for detecting contaminant particles. Inspection tools, such as a scanning electron microscope (SEM) are commonly used to inspect a partially fabricated device or wafer containing multiple devices for defects. For certain cases, it may be sufficient to image the defects, e.g., with the SEM and analyze the image to characterize defects. But for many cases, once defects have been detected it is important to chemically characterize them.
Those skilled in the substrate processing arts have long recognized the need for chemical characterization of very small defects. Unfortunately, many of the suggested defect characterization techniques do not provide chemical specific information. For example, Transmission Electron Microscopy (TEM) with energy dispersion x-ray (EDX) or energy-loss spectroscopy has been suggested for characterization of very small defects. Unfortunately, this technique does not provide chemical specific information and further requires a very thin sample for an electron beam to pass through. Scanning tunneling microscopy (STM) in conjunction with I-V curve or scanning near field optical spectroscopy has also been suggested. Although the sample need not be thin, the results do not provide chemical specific information.
An electron spectrometer utilizing a focusing field, such as a cylindrical mirror analyzer, is often used in spectroscopy of charged particles for chemical analysis that makes use of electrons emitted from a substance after being bombarded or irradiated with electrons or ions from a source such as an electron gun. Typical electron spectrometers operate in a scanning mode in which a voltage between two electrodes varies to selectively focus electrons of different energies onto a detector. An electron spectrum may be derived from a scan of detector signal as a function of voltage between the electrodes. Unfortunately, such scanning can take several minutes to complete. During this time, contaminants may build up on the sample and affect the spectrum. Consequently, most electron spectroscopy is done under ultra-high vacuum (UHV) condition (10−10 torr or less). However, UHV conditions require expensive equipment and considerable time. Thus, UHV electron spectroscopy is incompatible with semiconductor processing. It is within this context that embodiments of the present invention arise.